Makefile fixes

- to $( MAKE ) via variable when recursing the tree
- fix to honor the %- rules when more than 1 subdir is present
Makefile: setup rule to prepare the dev environment

- Recursing through llvm submod and configure and make

Signed-off-by: Benjamin Esquivel <benjaesq@me.com>
make ./configure on a need basis

-llvm takes forever to re-compile even if no change was made when
 ./configure is re-done. Now ./configure is only made when config.log
 doesn't exist
git submods and ./configure setup separated rules

-fixing ahead a bug when the repository is brand new and would try
 to ./configure without git submodule update --init
Makefile with llvm working example